JP7186652B2 - magnetocardiograph - Google Patents

Description

The present invention relates to a magnetocardiographic measuring device.

Conventionally, a magnetic field measurement device that measures the magnetic field emitted from the head or chest of a subject using a sensor platform board in which a plurality of Tunnel Magneto-Resistance (TMR) elements are arranged in an array is known ( For example, see Patent Document 1).
[Prior art documents]
[Patent Literature]
[Patent Document 1] JP 2012-152514 A

In a conventional magnetic field measurement device, a pair of magnetic detection elements are stacked in the magnetic field detection direction. , the disturbance magnetic field is suppressed based on the principle that the magnitude of the measurement result differs between a pair of magnetic detection elements, and the magnetic field to be measured is measured. However, in order to examine the state of the heart more precisely, magnetocardiography, which can more accurately measure the weak biomagnetic field (referred to as "magnetism") generated by the electrical activity of the heart, is needed. It would be desirable to implement a device.

In order to solve the above problems, a first aspect of the present invention provides a magnetocardiography apparatus. The magnetocardiographic measurement device may include a magnetic sensor array configured by three-dimensionally arranging a plurality of magnetic sensor cells each capable of detecting an input magnetic field in three axial directions. The magnetocardiographic measurement device may include a measurement data acquisition unit that acquires a measurement value based on an input magnetic field including magnetocardiography generated by electrical activity of the heart. The magnetocardiographic measurement device may include a gradient magnetic field calculator that calculates a gradient magnetic field using a plurality of measured values measured between a plurality of magnetic sensor cells. The magnetocardiographic measurement apparatus may include a signal space separation unit that uses a gradient magnetic field to separate the spatial distribution of the input magnetic field into the magnetocardiogram and the environmental magnetic field.

When the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function, the signal space separating unit divides a plurality of magnetic sensor cells into magnetic field signal vectors whose components are signals output by the magnetic sensors. The spatial distribution of the input magnetic field may be signal-separated using at least the magnetic field gradient vector calculated using the plurality of magnetic field signal vectors output between them as a basis vector.

The signal space separator may perform signal separation of the spatial distribution of the input magnetic field using the magnetic field gradient vector and the magnetic field signal vector as basis vectors.

Each of the plurality of magnetic sensor cells includes a magnetic sensor, a magnetic field generator that provides the magnetic sensor with a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor, and a current that the magnetic field generator flows to generate the feedback magnetic field. and an output for outputting an output signal.

The magnetic sensor may have a magnetoresistive element.

Each of the plurality of magnetic sensor cells may further have two magnetic flux concentrators arranged at both ends of the magnetoresistive effect element, and the magnetoresistive effect element may be arranged at a position sandwiched between the two magnetic flux concentrators.

A coil for generating a feedback magnetic field may be wound around the magnetoresistive element and the two magnetic flux concentrators.

A plurality of AD converters for converting outputs of the plurality of magnetic sensor cells from analog to digital and outputting measured values may be further provided, and the plurality of AD converters may perform AD conversion according to a common sampling clock.

The magnetic sensor array may be configured by arranging a plurality of magnetic sensor cells so as to form an internal space surrounding at least a portion of the chest of the subject.

The plurality of magnetic sensor cells may be arranged in a generally arcuate cross-sectional view along the chest of the object to be measured around the center of gravity of the object to be measured.

The central angle of the arc may be greater than 180°.

It should be noted that the above summary of the invention does not list all the necessary features of the invention. Subcombinations of these feature groups can also be inventions.

1 shows the configuration of a magnetocardiographic measurement device 10 according to this embodiment. 2 shows the configuration of a magnetic sensor unit 110 according to this embodiment. The configuration and arrangement of magnetic sensor cells 220 in the magnetic sensor array 210 according to the present embodiment are shown. 1 shows an example of input/output characteristics of a magnetic sensor having a magnetoresistance effect element according to this embodiment. 3 shows a configuration example of a sensor unit 300 according to the present embodiment. An example of input/output characteristics of the sensor unit 300 according to the present embodiment is shown. 4 shows a configuration example of a magnetic sensor 520 according to the present embodiment. FIG. 5 shows a magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to this embodiment. 2 shows the configurations of a magnetic sensor array 210, a sensor data collection unit 230, and a sensor data processing unit 900 according to the present embodiment. 4 shows a flow of calculation of the Nth-order gradient magnetic field by the magnetocardiography apparatus 10 according to the present embodiment. A flow of signal separation of the spatial distribution of the magnetic field by the magnetocardiography apparatus 10 according to the present embodiment is shown. 1 shows a flow in which the magnetocardiography apparatus 10 according to the present embodiment calculates an index ε and performs control based on the index ε. An example is shown in which the magnetocardiography apparatus 10 according to a modification of the present embodiment measures magnetocardiography using a magnetic sensor array 210 configured to form an internal space. An example in which the magnetocardiography apparatus 10 according to another modification of the present embodiment measures magnetocardiography using a magnetic sensor array 210 configured to form an internal space is shown. An example computer 2200 is shown in which aspects of the present invention may be embodied in whole or in part.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.

FIG. 1 shows the configuration of a magnetocardiography apparatus 10 according to this embodiment. The magnetocardiography apparatus 10 uses a magnetoresistance effect element to measure magnetocardiography, which is a magnetic field generated by electrical activity of the human heart. The magnetocardiography apparatus 10 may also be used to measure the magnetocardiography of a living body other than a human being.

The magnetocardiography device 10 includes a main body 100 and an information processing section 150 . The body section 100 is a component for sensing the magnetocardiogram of a subject (subject), and has a magnetic sensor unit 110 , a head 120 , a drive section 125 , a base section 130 and a pole section 140 .

The magnetic sensor unit 110 is arranged at a position on the subject's chest facing the heart during the magnetocardiogram measurement, and senses the magnetocardiogram of the subject. The head 120 supports the magnetic sensor unit 110 and makes the magnetic sensor unit 110 face the subject. The drive unit 125 is provided between the magnetic sensor unit 110 and the head 120, and changes the orientation of the magnetic sensor unit 110 with respect to the head 120 when performing calibration. The drive unit 125 according to the present embodiment includes a first actuator capable of rotating the magnetic sensor unit 110 360 degrees around the Z-axis in the drawing, an axis perpendicular to the Z-axis (in the state in the drawing, the X-axis ), which are used to change the azimuth and zenith angles of the magnetic sensor unit 110 . As shown as drive unit 125 in the drawing, drive unit 125 has a Y-shape when viewed from the Y-axis direction in the drawing, and the second actuator rotates magnetic sensor unit 110 360 degrees around the X-axis in the drawing. can be rotated.

The base part 130 is a base for supporting other parts, and in this embodiment, it is a stand on which a subject stands during magnetocardiographic measurement. The pole portion 140 supports the head 120 at the height of the subject's chest. The pole section 140 may be vertically extendable to adjust the height of the magnetic sensor unit 110 to the height of the subject's chest.

The information processing section 150 is a component for processing measurement data from the main body section 100 and outputting the data by display, printing, or the like. The information processing unit 150 may be a computer such as a PC (personal computer), a tablet computer, a smart phone, a workstation, a server computer, or a general-purpose computer, or may be a computer system in which multiple computers are connected. Alternatively, the information processing unit 150 may be a dedicated computer designed for information processing of magnetocardiography, or may be dedicated hardware implemented by a dedicated line.

FIG. 2 shows the configuration of the magnetic sensor unit 110 according to this embodiment. The magnetic sensor unit 110 has a magnetic sensor array 210 and a sensor data acquisition section 230 . The magnetic sensor array 210 is configured by three-dimensionally arranging a plurality of magnetic sensor cells 220 each having a plurality of magnetoresistance effect elements and capable of detecting input magnetic fields in three axial directions. In this figure, the magnetic sensor array 210 includes a plurality of magnetic sensor cells 220 in each of the X, Y, and Z directions (e.g., 8 in the X direction, 8 in the Y direction, and 2 in the Z direction, totaling 128 cells). magnetic sensor cells 220) are arranged in a plane.

The sensor data collection unit 230 is electrically connected (not shown) to the plurality of magnetic sensor cells 220 included in the magnetic sensor array 210, collects sensor data (detection signals) from the plurality of magnetic sensor cells 220, and collects information. It is supplied to the processing section 150 .

FIG. 3 shows the configuration and arrangement of the magnetic sensor cells 220 in the magnetic sensor array 210 according to this embodiment. Each magnetic sensor cell 220 has a plurality of sensor sections 300x-z (collectively referred to as "sensor sections 300") each having a magnetoresistive element. The sensor unit 300x is arranged along the X-axis direction and can detect a magnetic field in the X-axis direction. Further, the sensor unit 300y is arranged along the Y-axis direction and can detect a magnetic field in the Y-axis direction. Also, the sensor unit 300z is arranged along the Z-axis direction and can detect a magnetic field in the Z-axis direction. As shown by the enlarged view indicated by the dashed-dotted line in this figure, in this embodiment, each sensor unit 300 has a magnetic flux concentrator arranged at both ends of the magnetoresistive effect element. Therefore, each sensor unit 300 samples the spatial distribution of the magnetic field using the magnetoresistive effect element arranged at a narrow position sandwiched between the magnetic flux concentrators, thereby clearly sampling points in space in each axial direction. can do. The details of the configuration of each sensor unit 300 will be described later.

In this figure, the three-axis directions of the magnetic fields detected by the sensor units 300x, 300y, and 300z are the same as the three-dimensional directions in which the magnetic sensor cells 220 are arranged. This facilitates understanding of each component of the distribution of the measured magnetic field. In each magnetic sensor cell 220, the three sensor units 300x, 300y, and 300z do not overlap each other when viewed from the three-dimensional directions in which the magnetic sensor cells 220 are arranged, and are provided between the three sensor units 300. It is preferable that one end is provided on the gap side and the other end is arranged so as to extend in each of the three axial directions away from the gap. As an example, in this figure, a gap is provided in the lower left corner of the magnetic sensor cell 220 when viewed from the front. An example of extending in each of the X-axis, Y-axis, and Z-axis directions so as to separate from the gap is shown. In this figure, sensor units 300x, 300y, and 300z are arranged from one corner of a cubic magnetic sensor cell 220 along three sides perpendicular to each other, and a gap is provided in the one corner. However, the three-axis directions of the magnetic field to be detected and the three-dimensional directions in which the magnetic sensor cells 220 are arranged may be different. For example, the r-axis, the θ-axis, and the φ-axis of a polar coordinate system may be used instead of the X-axis, Y-axis, and Z-axis as the three-axis directions of the magnetic field to be detected. Also, as the three-dimensional directions in which the magnetic sensor cells 220 are arranged, the r-axis, the θ-axis, and the φ-axis of the polar coordinate system may be used instead of the X-axis, Y-axis, and Z-axis. When the three-axis directions of the magnetic field to be detected are different from the three-dimensional directions in which the magnetic sensor cells 220 are arranged, the arrangement of the sensor units 300 in the magnetic sensor cells 220 and the arrangement direction of the magnetic sensor cells 220 are not restricted. The degree of freedom in designing the sensor array 210 can be increased.

FIG. 4 shows an example of input/output characteristics of a magnetic sensor having a magnetoresistive element according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the magnetic sensor, and the vertical axis indicates the magnitude V_xMR0 of the detection signal of the magnetic sensor. The magnetic sensor has, for example, a giant magnetoresistance (GMR: Giant Magneto-Resistance) effect element or a tunnel magnetoresistance (TMR: Tunnel Magneto-Resistance) effect element, etc., and detects the magnitude of a predetermined uniaxial magnetic field. To detect.

Such a magnetic sensor has high magnetic sensitivity, which is the gradient of the detection signal V_xMR0 with respect to the input magnetic field B, and can detect a minute magnetic field of about 10 pT. On the other hand, in the magnetic sensor, for example, the detection signal V_xMR0 is saturated when the absolute value of the input magnetic field B is about 1 μT, and the range in which the linearity of the input/output characteristics is good is narrow. Therefore, by adding a closed loop that generates a feedback magnetic field to such a magnetic sensor, the linearity of the magnetic sensor can be improved. Such a magnetic sensor will be described below.

FIG. 5 shows a configuration example of the sensor unit 300 according to this embodiment. The sensor section 300 is provided inside each of the plurality of magnetic sensor cells 220 and includes a magnetic sensor 520 , a magnetic field generation section 530 and an output section 540 . A part of the sensor section 300, for example, the amplifier circuit 532 and the output section 540, may be provided on the sensor data collection section 230 side instead of the magnetic sensor cell 220 side.

The magnetic sensor 520 has a magnetoresistive element such as a GMR element or a TMR element, like the magnetic sensor described with reference to FIG. Each of the magnetic sensors 520 includes a magnetoresistive element and two magnetic flux concentrators arranged at both ends of the magnetoresistive element, and the magnetoresistive element is positioned between the two magnetic flux concentrators. placed. When the positive direction of the magnetic sensing axis is the +X direction, the magnetoresistance effect element of the magnetic sensor 520 increases in resistance when a magnetic field in the +X direction is input, and decreases in resistance when a magnetic field in the −X direction is input. may be configured to decrease. That is, the magnitude of the magnetic field B input to the magnetic sensor 520 can be detected by observing the change in the resistance value of the magnetoresistive element of the magnetic sensor 520 . For example, if the magnetic sensitivity of the magnetic sensor 520 is S, the detection result for the input magnetic field B of the magnetic sensor 520 can be calculated as S×B. As an example, the magnetic sensor 520 is connected to a power supply or the like, and outputs a voltage drop corresponding to a change in resistance value as a detection result of the input magnetic field. The details of the configuration of the magnetic sensor 520 will be described later.

The magnetic field generation section 530 generates a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor 520 with a magnitude corresponding to the output signal output by the output section 540 , and applies the feedback magnetic field to the magnetic sensor 520 . The magnetic field generator 530 operates to, for example, generate a feedback magnetic field B_FB that is opposite in direction to the magnetic field B input to the magnetic sensor 520 and has substantially the same absolute value as the input magnetic field, thereby canceling out the input magnetic field. Magnetic field generator 530 includes an amplifier circuit 532 and a coil 534 .

The amplifier circuit 532 outputs a current corresponding to the detection result of the input magnetic field of the magnetic sensor 520 as a feedback current I_FB. When the magnetoresistive element of the magnetic sensor 520 is composed of a bridge circuit including at least one magnetoresistive element, the input terminal pair of the amplifier circuit 532 is connected to the outputs of the bridge circuit. Then, the amplifier circuit 532 outputs a current corresponding to the output of the bridge circuit as the feedback current I_FB. The amplifier circuit 532 includes, for example, a transconductance amplifier, and outputs a feedback current I_FB corresponding to the output voltage of the magnetic sensor 520. FIG. For example, if the voltage-current conversion coefficient of the amplifier circuit 532 is G, the feedback current I_FB can be calculated as G×S×B.

Coil 534 generates a feedback magnetic field B_FB corresponding to feedback current I_FB. The coil 534 is wound along the axial direction of the magnetic field to be detected by the magnetic sensor 520 so as to surround the magnetoresistive element of the magnetic sensor 520 and the two magnetic flux concentrators arranged at both ends of the magnetoresistive element. It is written. Coil 534 preferably generates a uniform feedback magnetic field B_FB across magnetic sensor 520 . For example, if the coil coefficient of the coil 534 is β, the feedback magnetic field B_FB can be calculated as β×I_FB. Here, since the feedback magnetic field B_FB is generated in a direction to cancel the input magnetic field B, the magnetic field input to the magnetic sensor 520 is reduced to BB_FB. Therefore, the feedback current I_FB is given by the following equation.

By solving the equation (1) for the feedback current I_FB, the value of the feedback current I_FB in the steady state of the sensor unit 300 can be calculated. Assuming that the magnetic sensitivity S of the magnetic sensor 520 and the voltage/current conversion coefficient G of the amplifier circuit 532 are sufficiently large, the following equation is calculated from the equation (1).

The output unit 540 outputs an output signal V_xMR corresponding to the feedback current I_FB that the magnetic field generation unit 530 flows to generate the feedback magnetic field B_FB. The output unit 540 has, for example, a resistive element with a resistance value R, and outputs a voltage drop caused by the feedback current I_FB flowing through the resistive element as an output signal V_xMR. In this case, the output signal V_xMR is calculated from the equation (2) as follows.

As described above, the sensor unit 300 generates a feedback magnetic field that reduces the magnetic field that is input from the outside, so that the magnetic field that is substantially input to the magnetic sensor 520 is reduced. As a result, the sensor unit 300 uses, for example, a magnetoresistive effect element having a characteristic of being non-linear and narrow in the operating magnetic field range as shown in FIG. can also prevent the detection signal V_xMR from being saturated. Input/output characteristics of the sensor unit 300 will be described below.

FIG. 6 shows an example of input/output characteristics of the sensor section 300 according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the sensor section 300, and the vertical axis indicates the magnitude V_xMR of the detection signal of the sensor section 300. FIG. The sensor unit 300 has high magnetic sensitivity and can detect a minute magnetic field of about 10 pT. Further, the sensor unit 300 can maintain good linearity of the detection signal V_xMR even if the absolute value of the input magnetic field B exceeds 100 μT, for example.

That is, in the sensor unit 300 according to the present embodiment, the detection result for the input magnetic field B has linearity in a predetermined range of the input magnetic field B, for example, the absolute value of the input magnetic field B is several hundred μT or less. configured as By using such a sensor unit 300, weak magnetic signals such as magnetocardiographic signals can be easily detected.

FIG. 7 shows a configuration example of a magnetic sensor 520 according to this embodiment. In this figure, the magnetic sensor 520 has a magnetoresistive element 710 and magnetic flux concentrators 720 and 730 arranged at both ends of the magnetoresistive element 710 . The magnetic flux concentrators 720 and 730 are arranged at both ends of the magnetoresistive element 710 so as to sandwich the magnetoresistive element 710 therebetween. In this figure, the magnetic flux concentrator plate 720 is provided on the negative side of the magnetoresistive effect element 710 along the magnetosensitive axis, and the magnetic flux concentrator plate 730 is provided on the positive side of the magnetoresistive effect element 710 along the magnetosensitive axis. It is Here, the magneto-sensitive axis may be along the magnetization direction fixed in the magnetization fixed layer forming the magnetoresistive element 710 . Also, when a magnetic field is input from the negative side to the positive side of the magnetosensitive axis, the resistance of the magnetoresistive element 710 may increase or decrease. The magnetic flux concentrator plates 720 and 730 are made of a material with high magnetic permeability such as Permalloy. When the magnetic sensor 520 is configured as shown in this figure, the coil 534 surrounds the cross section of the magnetoresistive effect element 710 and the magnetic converging plates 720 and 730 arranged at both ends of the magnetoresistive effect element 710. , the magnetic sensor 520 is wound along the axial direction of the magnetic field to be detected. Moreover, when the magnetic sensor 520 has a plurality of magnetoresistive elements 710 in one magnetic sensor 520, it may have a plurality of sets each including the magnetoresistive element and the magnetic flux concentrator arranged at both ends thereof. In that case, the coil 534 may be wound so as to surround the set including the magnetoresistive element and the magnetic flux concentrator arranged at both ends with one coil.

In such a magnetic sensor 520, when a magnetic field is input from the negative side to the positive side of the magnetosensitive axis, the magnetic flux concentrator plates 720 and 730 made of a material with high magnetic permeability are magnetized. A magnetic flux distribution is generated as indicated by the dashed line. Then, the magnetic flux generated by magnetizing the magnetic flux concentrators 720 and 730 passes through the magnetoresistive element 710 sandwiched between the two magnetic flux concentrators 720 and 730 . Therefore, the magnetic flux density at the position of the magnetoresistive element 710 can be greatly increased by arranging the magnetic flux concentrators 720 and 730 . Further, as shown in this figure, the spatial distribution of the magnetic field is sampled using the magnetoresistive effect element 710 arranged at a narrow position sandwiched between the magnetic converging plates 720 and 730, thereby clarifying the sampling points in the space. be able to.

FIG. 8 shows the magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to this embodiment. In FIG. 8, members having the same functions and configurations as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted except for differences. In the magnetic sensor 520 according to the present embodiment, when a feedback current is supplied to the coil 534, the coil 534 generates a feedback magnetic field, thereby generating a magnetic flux distribution as indicated by a dashed line in the figure. The magnetic flux generated by this feedback magnetic field is spatially distributed so as to cancel the spatial distribution of the magnetic field input to the magnetoresistive element 710 and magnetically amplified by the magnetic flux concentrators 720 and 730 . For this reason, the magnetic sensor 520 has magnetic converging plates 720 and 730 arranged at both ends of a magnetoresistive effect element 710 as shown in this figure, and includes the magnetoresistive effect element and the magnetic concentrating plates arranged at both ends thereof. When the coil 534 is wound so as to surround the set with one coil, the magnetic field distribution at the position of the magnetoresistive effect element 710 can be accurately canceled by the feedback magnetic field. It is possible to realize a sensor with high linearity between

FIG. 9 shows configurations of a magnetic sensor array 210, a sensor data collection unit 230, and a sensor data processing unit 900 according to this embodiment.

The magnetic sensor array 210 has multiple magnetic sensor cells 220 . Each of the multiple magnetic sensor cells 220 may have multiple sensor portions 300x-z as described above. In this figure, among the plurality of magnetic sensor cells 220 that the magnetic sensor array 210 has in each dimension, positions [i, j, k], [i+1, j, k], [i, j+1, k], and The part for [i,j,k+1] is shown.

The sensor data acquisition unit 230 has multiple AD converters 232 and clock generators 234 . The plurality of AD converters 232 convert the outputs of the plurality of magnetic sensor cells 220 from analog to digital and output measured values. As an example, the plurality of AD converters 232 are provided corresponding to each of the plurality of sensor units 300x to 300z of the magnetic sensor cell 220, and analog detection signals output by the corresponding sensor units 300 (sensor The output signal V_xMR) is converted into digital measurement values V (Vx, Vy, Vz), and a plurality of measurement values are output as measurement data. Here, Vx, Vy, and Vz are measured values (for example, digital voltage values) obtained by digitally converting the detection signals from the sensor units 300x, 300y, and 300z, respectively.

The clock generator 234 generates a sampling clock and supplies a common sampling clock to each of the AD converters 232 . Each of the AD converters 232 performs AD conversion according to the common sampling clock supplied from the clock generator 234 . Therefore, all of the plurality of AD converters 232 that AD-convert the outputs of the plurality of sensor units 300x to 300z provided at different positions perform synchronous operation. This allows the plurality of AD converters 232 to simultaneously sample the detection results of the plurality of sensor units 300x to 300z provided in different spaces.

The sensor data processing unit 900 includes a plurality of measurement data acquisition units 910 provided corresponding to each of the plurality of magnetic sensor cells 220, a plurality of calibration calculation units 920, a plurality of data output units 930, a gradient magnetic field calculation unit 940, a base It has a vector storage section 950 , a signal space separation section 960 , an index calculation section 970 , an index output section 980 and a fault determination section 990 .

The measurement data acquisition unit 910 acquires measurement values based on input magnetic fields including magnetocardia generated by electrical activity of the heart. The measurement data acquisition unit 910 is connected to three AD converters 232 that are connected to the corresponding magnetic sensor cells 220, and is measured by the sensor units 300x to 300z in the plurality of magnetic sensor cells 220 that make up the magnetic sensor array 210. A plurality of measurement values are obtained as measurement data. Specifically, the measurement data acquisition unit 910 may be configured using a flip-flop or the like that latches the measurement values V (Vx, Vy, Vz) digitally converted by the AD converter 232 at a predetermined timing T.

The calibration calculation unit 920 is connected to the measurement data acquisition unit 910 and calibrates the measurement data acquired by the measurement data acquisition unit 910 using calibration parameters. The outline of the calibration of the measurement data by the calibration calculator 920 is as follows. The magnetic field input to the magnetic sensor cell 220 at the position [i, j, k] is defined as B (Bx, By, Bz), and the detection results of the triaxial magnetic sensor by the sensor units 300x, 300y, and 300z are measured values V (Vx , Vy, Vz). In this case, assuming that the magnetic sensor characteristics of the triaxial magnetic sensor are a matrix S, the detection result V of the triaxial magnetic sensor can be expressed by the following equation.

Here, Sxx, Syy, and Szz represent the sensitivities of the sensor units 300x, 300y, and 300z in the main axis direction, respectively, and Sxy, Sxz, Syx, Syz, Szx, and Szy represent the sensitivities in the other axis directions. . Vos,x, Vos,y, and Vos,z represent offsets in the principal axis direction of the sensor units 300x, 300y, and 300z, respectively.

Each of the sensor units 300 has linearity in the detection result for the input magnetic field in the range of the input magnetic field to be detected. Become. Further, even if the sensor unit 300 has multi-axis sensitivity, if the detection result of the sensor unit 300 has linearity, each element of the matrix S is an approximation irrelevant to the magnitude of the input magnetic field B. constant coefficient.

Therefore, the calibration calculation unit 920 uses the inverse matrix S ⁻¹ of the matrix S and the offset (Vos, x, Vos, y, Vos, z) to obtain the measured value V (Vx, Vy , Vz) can be converted to a magnetic field measurement B(Bx,By,Bz) that represents the original input magnetic field. Note that this conversion is also established when the sensor units 300x to 300z are provided with the magnetic flux concentrators described above. This is because the magnetic sensor cell 220 is configured as a three-axis magnetic sensor using the sensor units 300x to 300z, and conversion using linear algebra is possible.

The calibration calculation unit 920 uses the environmental magnetic field measurement data to calculate the inverse matrix S ⁻¹ of the matrix S and the offset (Vos, x, Vos, y, Vos, z) acquired by the measurement data acquisition unit 910. The measurements V are converted to magnetic field measurements B using these calibration parameters. Then, the calibration calculation section 920 supplies the plurality of magnetic field measurement values B to the data output section 930 as magnetic field measurement data.

As described above, since each sensor unit 300 has linearity, the calibration calculation unit 920 can convert the measured value V into the magnetic field measured value B using a substantially constant coefficient. That is, the substantially constant coefficients used by the calibration calculator 920 can be determined as a set of calibration parameters using environmental magnetic field data.

The data output section 930 supplies the plurality of magnetic field measurement values B calibrated by the calibration calculation section 920 to the gradient magnetic field calculation section 940 as magnetic field measurement data.

The gradient magnetic field calculator 940 calculates the gradient magnetic field using multiple measured values measured between the multiple magnetic sensor cells 220 . For example, the gradient magnetic field calculator 940 calculates the gradient magnetic field using the magnetic field measurement data supplied from the data output section 930 . In this embodiment, the gradient magnetic field calculator 940 calculates gradient magnetic fields in all three-dimensional directions for all magnetic fields in three axial directions. This makes it possible to obtain a more detailed gradient magnetic field distribution. Alternatively, the gradient magnetic field calculator 940 may calculate gradient magnetic fields only for some magnetic fields in three axial directions. Further, the gradient magnetic field calculator 940 may calculate the gradient magnetic field only for a part of the three-dimensional directions. As a result, only the necessary gradient magnetic field components can be calculated, and the computational processing load in the gradient magnetic field computing section 940 can be reduced.

Further, in this embodiment, the three-axis directions of the magnetic field to be detected and the three-dimensional directions in which the magnetic sensor cells 220 are arranged are the same. This facilitates the calculation for separating the signals in the signal space separation described later. Alternatively, the three-axis directions of the magnetic field to be detected and the three-dimensional directions in which the magnetic sensor cells 220 are arranged may be different. When both are different, the arrangement of the sensor units 300 in the magnetic sensor cells 220 and the arrangement direction of the magnetic sensor cells 220 are not restricted, and the degree of freedom in designing the magnetic sensor array 210 can be increased.

The gradient magnetic field calculator 940 calculates the difference in the magnetic field between the adjacent magnetic sensor cells 220 using the magnetic field measurement data measured between the adjacent magnetic sensor cells 220 of the plurality of magnetic sensor cells 220, that is, the magnetic field measurement. By calculating the difference in value B, the gradient magnetic field is calculated. The gradient magnetic field calculator 940 may calculate a gradient magnetic field of second or higher order using magnetic field measurement data measured between a plurality of adjacent magnetic sensor cells 220 . This will be discussed later. The gradient magnetic field calculation unit 940 supplies the calculated gradient magnetic field to the basis vector storage unit 950 and the signal space separation unit 960 together with the magnetic field measurement data.

The basis vector storage unit 950 stores basis vectors necessary for the signal space separation unit 960 to separate the spatial distribution of the magnetic field. In this case, the basis vector storage unit 950 stores, as the magnetic field signal vector, a vector whose components are signals output from each of the magnetic sensors 520 when the magnetic sensor array 210 detects a magnetic field having a spatial distribution of orthonormal functions. Furthermore, magnetic field gradient vectors calculated using a plurality of magnetic field signal vectors output between a plurality of magnetic sensor cells 220 may be stored at least as basis vectors. In addition to the magnetic field gradient vector, the basis vector storage unit 950 may store the magnetic field signal vector used to calculate the magnetic field gradient vector as a basis vector. The basis vector storage unit 950 supplies the stored basis vectors to the signal space separation unit 960 .

The signal space separation unit 960 uses the gradient magnetic field to separate the spatial distribution of the input magnetic field into the magnetocardiogram and the environmental magnetic field. The signal space separation unit 960 divides a magnetic field signal vector into a plurality of The spatial distribution of the input magnetic field may be signal-separated using at least the magnetic field gradient vector calculated using the plurality of magnetic field signal vectors output between the magnetic sensor cells 220 as a basis vector. At this time, the signal space separation unit 960 may separate the spatial distribution of the input magnetic field into signals using the magnetic field gradient vector and the magnetic field signal vector as base vectors. As an example, the signal space separation unit 960 extracts the spatial distribution of the magnetic field indicated by the magnetic field measurement data calibrated by the calibration calculation unit 920 and the gradient magnetic field calculated by the gradient magnetic field calculation unit 940 from the basis vector storage unit 950. Signal separation is performed using the supplied magnetic field signal vector and magnetic field gradient vector as basis vectors. This will be discussed later. The signal space separation unit 960 supplies the result of spatially separating the magnetic field to the index calculation unit 970 .

The index calculator 970 calculates an index ε indicating the accuracy of calibration in the calibration calculator 920 . The index calculator 970 is connected to the signal space separator 960 and calculates the index ε based on the signal separation result of the signal space separator 960 .

The index output section 980 is connected to the index calculation section 970 and outputs the index ε calculated by the index calculation section 970 . At this time, the index output unit 980 may, for example, display the index ε on the display unit, or may supply the index ε to another device via the network. Also, the index output unit 980 supplies the index ε to the failure determination unit 990 as shown in the figure.

The failure determination unit 990 determines failure of the magnetocardiography device 10 based on the index ε calculated by the index calculation unit 970 .

FIG. 10 shows a flow of calculation of the Nth-order gradient magnetic field by the magnetocardiography apparatus 10 according to this embodiment. At step 1010, the gradient magnetic field calculator 940 substitutes 1 for n. At step 1020, the gradient magnetic field calculator 940 acquires the magnetic field measurement value B measured by the magnetic sensor cell 220 at each position. Here, the magnetic field measurement value B measured by the magnetic sensor cell 220 at the position [i, j, k] is expressed as in the following equation (6).

In step 1030, the gradient magnetic field calculator 940 uses the magnetic field measurement value B between adjacent magnetic sensor cells 220 included in the magnetic sensor array 210 to calculate the first-order difference in the magnetic field, thereby obtaining the first-order gradient magnetic field. Calculate The gradient magnetic field calculator 940 calculates the first-order gradient magnetic field in the X-axis direction from the magnetic field measurement data measured between the magnetic sensor cell 220 [i+1, j, k] and the magnetic sensor cell 220 [i, j, k]. It is calculated by the following formula using

That is, the gradient magnetic field calculator 940 calculates the X-axis magnetic field measurement value Bx i+1, ^{j, k} of the magnetic sensor cell 220 [i+1, j, k] from the X-axis magnetic field measurement value Bx i+1, j, k of the magnetic sensor cell 220 [i, j, k]. Bx ^i,j,k is subtracted to calculate the difference in the X-axis component of the magnetic field measurement value between the magnetic sensor cell 220[i+1,j,k] and the magnetic sensor cell 220[i,j,k]; Dividing by the distance Δx between magnetic sensor cell 220[i+1,j,k] and magnetic sensor cell 220[i,j,k] gives the X-axis component of the magnetic field measurement at position [i,j,k]: A first-order gradient magnetic field in the X-axis direction is calculated.

Similarly, the gradient magnetic field calculator 940 calculates the Y-axis magnetic field measurement value By i+1, ^{j, k} of the magnetic sensor cell 220 [i+1, j, k] from the Y-axis magnetic field measurement value By i+1, j, k of the magnetic sensor cell 220 [i, j, k]. By subtracting the value By ^i,j,k to calculate the difference in the Y-axis component of the magnetic field measurement between magnetic sensor cell 220[i+1,j,k] and magnetic sensor cell 220[i,j,k]; by the distance Δx between magnetic sensor cell 220[i+1,j,k] and magnetic sensor cell 220[i,j,k] yields the Y-axis component of the magnetic field measurement at position [i,j,k] Calculate the first-order gradient magnetic field in the X-axis direction with respect to .

Similarly, the gradient magnetic field calculator 940 calculates the Z-axis magnetic field measurement value Bz ^{i+1, j, k} of the magnetic sensor cell 220 [i+1, j, k] from the Z-axis magnetic field measurement value Bz i+1, j, k of the magnetic sensor cell 220 [i, j, k]. subtracting the value Bz ^i,j,k to calculate the difference in the Z-axis component of the magnetic field measurement between the magnetic sensor cell 220[i+1,j,k] and the magnetic sensor cell 220[i,j,k]; by the distance Δx between magnetic sensor cell 220[i+1,j,k] and magnetic sensor cell 220[i,j,k], the Z-axis component of the magnetic field measurement at position [i,j,k] Calculate the first-order gradient magnetic field in the X-axis direction with respect to .

In addition, the gradient magnetic field calculator 940 calculates the primary gradient magnetic field in the Y-axis direction in the same manner as the primary gradient magnetic field in the X-axis direction, the magnetic sensor cell 220[i, j+1, k] and the magnetic sensor cell 220[ i, j, k] using the magnetic field measurement values measured by the following equation.

In addition, the gradient magnetic field calculator 940 calculates the first-order gradient magnetic field in the Z-axis direction in the same manner as the first-order gradient magnetic field in the X-axis direction. i, j, k] using the magnetic field measurement values measured by the following equation.

The gradient magnetic field calculator 940 can obtain the following first-order gradient magnetic field in the three-dimensional direction with respect to the three-axis magnetic field measurement values by the calculations of formulas (7) to (9). Note that the gradient magnetic field calculator 940 may calculate the primary gradient magnetic field using the distance Δx=Δy=Δz between the magnetic sensor cells 220 as one unit. In this case, the gradient magnetic field calculator 940 can regard the difference in magnetic field measurement data as a primary gradient magnetic field.

At step 1040, the gradient magnetic field calculator 940 determines whether or not n is equal to N. If n is equal to N, gradient magnetic field calculator 940 terminates the process. In step 1040, if n is not equal to N, the gradient magnetic field calculator 940 advances the process to step 1050 and increments n by one. Gradient magnetic field calculator 940 then advances the process to step 1060 .

In step 1060, the gradient magnetic field calculator 940 calculates the nth-order gradient magnetic field using the (n−1)th-order gradient magnetic field of the magnetic field. As an example, in step 1030 before calculating the secondary gradient magnetic field, the gradient magnetic field calculator 940 adds the formula (7) to the magnetic sensor cell 220 [i+2, j , k] and the magnetic sensor cell 220 [i+1, j, k], the first-order gradient magnetic field at position [i+1, j, k] has been calculated by the following equation: be.

Therefore, in step 1060 when calculating the second-order gradient magnetic field, the gradient magnetic field calculator 940 calculates the X-axis A second-order gradient magnetic field is calculated with respect to the direction.

That is, the gradient magnetic field calculator 940 subtracts the first-order gradient magnetic field in the X-axis direction at position [i, j, k] from the first-order gradient magnetic field in the X-axis direction at position [i+1, j, k]. By dividing the obtained value by the distance ΔX between adjacent magnetic sensor cells 220 in the X-axis direction, the secondary gradient magnetic field in the X-axis direction is calculated.

The gradient magnetic field calculator 940 can also calculate secondary gradient magnetic fields in the Y-axis direction and the Z-axis direction by performing the same calculation as in the X-axis direction. Next, the gradient magnetic field calculator 940 returns the process to step 1040 and repeats the process thereafter. As a result, the gradient magnetic field calculator 940 can obtain the n-th gradient magnetic field in the three-dimensional direction with respect to the three-axis magnetic field measurement values using the magnetic field measurement values measured between the adjacent magnetic sensor cells 220. can.

Here, when N=1, the gradient magnetic field calculator 940 assumes that Δx=Δy=Δz is sufficiently small, and converts the first-order gradient magnetic field given by the equation (10) obtained in step 1030 as follows: can be represented.

When N=2, the gradient magnetic field calculator 940 acquires the following secondary gradient magnetic field from the primary gradient magnetic field and the flow of this figure.

When N is greater than 2, the gradient magnetic field calculator 940 acquires the following n-th gradient magnetic field from the primary and secondary gradient magnetic fields and the flow of this figure.

As described above, according to the magnetocardiography apparatus 10 of the present embodiment, as shown in equations (13), (14), and (15), three-dimensional directions for the three-axis magnetic field measurement values can be obtained completely. Further, according to the magnetocardiography apparatus 10 of the present embodiment, calculation is performed from the magnetic field between the adjacent magnetic sensor cells 220, so only the secondary or higher gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction are calculated. However, we can also obtain the gradient magnetic field components corresponding to the forms partially differentiated in different axial directions, such as ^∂2B /∂x∂y, ^∂2B /∂y∂z, and ^∂2B /∂z∂x. . Then, the magnetocardiography apparatus 10 of the present embodiment uses at least part of the gradient magnetic field thus obtained to separate the spatial distribution of the input magnetic field into the magnetocardiogram and the environmental magnetic field.

FIG. 11 shows a flow of signal separation of the spatial distribution of the magnetic field by the magnetocardiography apparatus 10 according to this embodiment. At step 1110, the magnetocardiography apparatus 10 calculates a magnetic field gradient vector. For example, the gradient magnetic field calculation unit 940 of the magnetocardiographic measurement device 10 detects a magnetic field having a spatial distribution of an orthonormal function with the magnetic sensor array 210 before the magnetocardiographic measurement, and each of the plurality of magnetic sensors 520 outputs A vector whose component is the signal to be applied is obtained as a magnetic field signal vector. Note that the orthonormal functions may be, for example, spherical harmonic functions. As an example, the gradient magnetic field calculator 940 acquires a magnetic field signal vector obtained by spatially sampling spherical harmonics when a predetermined point in space is specified as the coordinate origin before magnetocardiogram measurement. Here, the spherical harmonic function is a function obtained by restricting a homogeneous polynomial, which is a solution of the n-dimensional Laplace's equation, to the unit sphere, and has orthonormality on the sphere. Then, the gradient magnetic field calculator 940 calculates magnetic field gradient vectors using the plurality of magnetic field signal vectors output between the plurality of magnetic sensor cells 220 according to the flow of FIG. At this time, the gradient magnetic field calculation unit 940 may calculate a primary magnetic field gradient vector or a secondary or higher magnetic field gradient vector according to the flow of FIG. The gradient magnetic field calculator 940 then supplies the calculated magnetic field gradient vector to the basis vector storage unit 950 together with the magnetic field signal vector used to calculate the magnetic field gradient vector.

At step 1120, the magnetocardiography apparatus 10 stores the basis vectors. For example, the basis vector storage unit 950 of the magnetocardiography apparatus 10 stores the magnetic field gradient vectors supplied from the gradient magnetic field calculation unit 940 as basis vectors together with the magnetic field signal vectors used to calculate the magnetic field gradient vectors. In this figure, as an example, step 1110 in which the gradient magnetic field calculation unit 940 calculates the magnetic field gradient vector and step 1120 in which the basis vector storage unit 950 stores the basis vector are performed by the magnetocardiography device 10. A case where the spatial distribution is taken as the first step in the flow of signal separation is shown. However, before the flow of signal separation of the spatial distribution of the magnetic field by the magnetocardiography apparatus 10, the gradient magnetic field calculation unit 940 calculates the magnetic field gradient vector in advance, and the basis vector storage unit 950 stores the basis vector in advance. You can keep it. Further, the basis vector storage unit 950 may store a magnetic field gradient vector determined in advance based on a simulation result or the like as a basis vector together with the magnetic field signal vector.

At step 1130, the magnetocardiography apparatus 10 measures magnetocardiography. For example, the subject is allowed to stand on the base section 130 and the subject's chest is placed at a position facing the magnetic sensor unit 110 . Then, in the state of sensing the magnetocardiogram of the subject, the signal space separation unit 960 combines the magnetic field measurement data calibrated by the calibration calculation unit 920 with the gradient magnetic field calculated by the gradient magnetic field calculation unit 940. Get from

At step 1140, the magnetocardiography apparatus 10 acquires basis vectors. For example, the signal space separation unit 960 acquires from the basis vector storage unit 950 the basis vectors stored in the basis vector storage unit 950 in step 1120 . In this flow, either step 1130 or step 1140 may be performed first.

At step 1150 , the magnetocardiography apparatus 10 separates the spatial distribution of the magnetic field measured at step 1130 into signals. For example, the signal space separation unit 960 uses the magnetic field signal vector and the magnetic field gradient vector obtained in step 1140 as basis vectors for the spatial distribution of the magnetic field indicated by the magnetic field measurement data and the gradient magnetic field obtained in step 1130. Series expansion. Then, the signal space separation unit 960 separates the spatial distribution of the measured magnetic field into the magnetocardiogram and the disturbance magnetic field from the vector obtained by the series expansion.

Then, the signal space separator 960 suppresses the disturbance magnetic field and extracts only the magnetocardiogram from the result of the signal separation. This will be described in detail below using mathematical formulas.

The static magnetic field B(r) is determined as the spatial gradient of the potential V(r) as follows using the potential V(r) that satisfies the Laplace equation Δ·V(r)=0. Here, r is a position vector representing a position from the coordinate origin, Δ is the Laplacian, μ is magnetic permeability, and ∇ is an operator representing vector differential operation.

Since the solution of Laplace's equation generally has a solution in the form of a series expansion using spherical harmonic functions Yl,m(θ,φ), which is an orthonormal function system, the potential V(r) is expressed by the following equation: can be represented. where |r| is the absolute value of the position vector r (distance from the coordinate origin), θ and φ are the two declination angles in spherical coordinates, l is the azimuthal quantum number, and m is the magnetic quantum number. where α and β are the multipolar moments, and Lin and Lout are series numbers for the space in front of and behind the magnetic sensor array 210 as seen from the coordinate origin and the subject, respectively. The azimuthal quantum number l takes a positive integer, and the magnetic quantum number m takes an integer from -1 to +1. That is, for example, when l is 1, m is -1, 0, and 1, and when l is 2, m is -2, -1, 0, 1, and 2. Since there is no single magnetic pole in the magnetic field, the azimuthal quantum number l in Equation (17) starts from 1, not from 0. The first term in (Equation 17) is a term that is inversely proportional to the distance from the coordinate origin, and indicates the potential that exists in the space in front of the magnetic sensor array 210 as viewed from the coordinate origin and the subject. The second term in (Equation 17) is a term proportional to the distance from the coordinate origin, and indicates the potential existing in the space behind the magnetic sensor array 210 as viewed from the coordinate origin and the subject.

Therefore, according to (Equation 16) and (Equation 17), the static magnetic field B(r) can be expressed by the following equation. Here, the first term in (Equation 18) indicates the magnetic field source existing in the space in front of the magnetic sensor array 210 as viewed from the coordinate origin and the subject, that is, the magnetocardiogram produced by the electrical activity of the heart. The second term in (Equation 18) indicates the disturbance magnetic field generated by the magnetic field source existing in the space behind the magnetic sensor array 210 as seen from the coordinate origin and the subject.

When the solution of Laplace's equation is expressed in the form of a series expansion using spherical harmonics, the general solution becomes an infinite series. It is sufficient to obtain the ratio of the magnetic field signal to be measured to the magnetic field and the sensor noise, and in fact, it is said that a series of about 10 terms is sufficient. In addition, it is said that about Lin=8 and Lout=3 are sufficient for the series of signal spatial separation in the magnetoencephalography. Therefore, in the magnetocardiography apparatus 10 of the present embodiment as well, the case of Lin=8 and Lout=3 will be described as an example. However, the values of Lin and Lout are not limited to these, and may be any values that are sufficient to sufficiently suppress the disturbance magnetic field and extract only the magnetocardiogram to be measured.

Here, let nx, ny, and nz be vectors representing the magnetosensitive axis directions and magnetic sensitivities of sensor units 300x, y, and z in each magnetic sensor cell 220, respectively, and subscript t be a transposed matrix, and al, m, and bl,m are defined as follows. That is, al, m and bl, m are the vectors nx, ny, and nz representing the magnetosensitive axis directions and magnetic sensitivities of the sensor units 300x, y, and z, and the spherical harmonic functions, which are three-dimensional vector signals. It is defined as a vector with inner products as components. This means sampling the spherical harmonics in a Cartesian coordinate system. In the present embodiment, al, m and bl, m are vectors having a dimension obtained by adding the number of the gradient magnetic fields calculated by the gradient magnetic field calculator 940 to the number obtained by multiplying the number of the magnetic sensor cells 220 by three. Become. Thus, in this embodiment, the basis vector storage unit 950 stores the values of al,m and bl,m including the gradient magnetic fields calculated by the gradient magnetic field calculation unit 940 . The magnetocardiography apparatus 10 according to the present embodiment, in which the basis vector storage unit 950 stores the values of al, m and bl, m including the gradient magnetic field, calculates from actual data actually measured by the sensor unit during operation. The gradient distribution of the magnetic field obtained can be used to virtually supplement the magnetic field information at locations where there is no real data. The vectors nx, ny, and nz representing the magnetosensitive axis direction and the magnetic sensitivity of each sensor unit 300 may be vectors corresponding to the above-described sensitivity in the main axis direction and the sensitivity in the other axis direction. nx may correspond to Sxx, Sxy, Sxz. ny may correspond to Syx, Syy, Syz. nz may correspond to Szx, Szy, Szz. Thus, the base vector storage unit 950 stores the values of al,m and bl,m calculated including the sensitivities of the sensor units 300 x, y, and z in the main axis direction and the sensitivity corrections in the other axis directions. The magnetocardiography apparatus 10 according to the present embodiment, in which the basis vector storage unit 950 stores the values of al, m and bl, m calculated including the correction of the magnetic sensitivity (main axis sensitivity, other axis sensitivity), operates In some cases, the measurement data acquired by the measurement data acquisition unit 910 is corrected by the calibration calculation unit 920, so that the magnetic sensitivity (main axis sensitivity, other axis sensitivity) of each magnetic sensor cell 220 can be corrected. Become.

Then, the output vector Φ of the magnetic field measured using the magnetic sensor array 210 at a certain time, that is, the output vector Φ indicated by the magnetic field measurement data and the gradient magnetic field can be expressed by the following equation.

Further, Sin, Sout, Xin, and Xout are defined as follows. That is, a total of Lin·(Lin+2) columns of vectors, in which each vector a when Sin is an integer from l=1 to l=Lin and m=-l to l is arranged in order in each l defined as In addition, Sout is a vector of Lout (Lout+2) columns in which each vector b when taking an integer from l = 1 to L = Lout and m = -l to l for each l is arranged in order. defined as In addition, Xin is a total of Lin· Define a vector with (Lin+2) rows. In addition, Xout is a total of Lout· Define a vector with (Lout+2) rows.

Then, the output vector Φ can be expressed in the form of the inner product of the matrix S and the column vector X as shown in the following equation. Here, the matrix S indicates a matrix obtained by arranging a total of Lin·(Lin+2)+Lout·(Lout+2) basis vectors as vertical vectors. It is obtained from the unit 950 . A vertical vector X indicates coefficients related to basis vectors.

In step 1150, the signal space separation unit 960 according to the present embodiment uses the following equation to approximate Φ = S · X based on the model formula of the output vector Φ obtained in (Equation 22). Determine the vertical vector X that fills with . This allows the signal space separator 960 to solve the spatial distribution of the magnetic field in step 1150 . At this time, when the magnitude of the disturbance magnetic field exceeds a predetermined range, the signal space separation unit 960 may issue a warning that the magnetocardiogram, which is the magnetic field to be measured, cannot be measured with high accuracy. As a result, the magnetocardiography apparatus 10 can measure the magnetocardiography in a situation such as when the apparatus is out of order or when there is a disturbance magnetic field that is so large that the magnetic field to be measured cannot be measured with high accuracy. You can prevent it from happening in advance. In this case, the signal space separation unit 960 determines that the magnitude of the disturbance magnetic field exceeds a predetermined range, for example, when the magnitude of any one of the components of Xout and Sout exceeds a predetermined threshold. Alternatively, it may be determined that the magnitude of the disturbance magnetic field exceeds a predetermined range when the sum or average of the magnitudes of the components of Xout and Sout exceeds a predetermined threshold value.

Then, in step 1150, the signal space separation section 960 extracts only the magnetocardiogram component to be measured from the result of the spatial separation of the magnetic field. Here, regarding the vertical vector X determined by the signal space separation unit 960 using (Equation 22) and (Equation 23), Xin·Sin represents the magnetocardiogram component to be measured, and Xout·Sout represents the disturbance magnetic field component. show. Therefore, in order to eliminate the disturbance magnetic field component and extract only the magnetocardiogram component to be measured, the signal space separation unit 960 should extract only Xin·Sin from the magnetic field spatial separation result X·S.

In this way, the magnetocardiography apparatus 10 measures the spatial distribution of the magnetic field measured using the magnetic sensor array 210 having a plurality of magnetic sensor cells 220 each capable of detecting an input magnetic field in three axial directions, with the magnetic field to be measured. It is possible to separate the signal into a magnetocardiogram and a disturbance magnetic field, suppress the disturbance magnetic field component, and extract only the magnetocardiogram component. The magnetocardiography apparatus 10 according to the present embodiment uses a gradient magnetic field calculated using a plurality of measured values measured between a plurality of magnetic sensor cells 220 in signal separation of the spatial distribution of the magnetic field. As a result, the magnetocardiographic measurement apparatus 10 can virtually compensate for magnetic field information at a position where there is no actual data, that is, at a position where the sensor unit 300 is not actually arranged, thereby improving the accuracy of the magnetocardiographic measurement. can be done. For example, the magnetocardiographic measurement apparatus 10 can increase the apparent amount of information by using both the actual data actually measured and the gradient magnetic field calculated from the actual data, thereby improving the accuracy of the magnetocardiographic measurement. can be enhanced. For magnetocardiography, ideally, it is preferable to arrange the sensor unit 300 on a spherical surface at a position close to the heart so as to surround the heart. However, due to physical restrictions, it is extremely difficult to ideally arrange the sensor unit 300 . The magnetocardiographic measurement apparatus 10 according to the present embodiment can virtually compensate for magnetic field information even in such a situation, so that the magnetocardiogram can be measured with high accuracy. In addition, since each of the plurality of sensor units 300 has a magnetic flux converging plate, the magnetic sensitivity of the sensor unit 300 can be enhanced, and spatial sampling points can be clarified, thereby enhancing compatibility with signal spatial separation technology. can. Furthermore, when the magnetocardiographic measurement device 10 has the calibration calculation unit 920, highly accurate calibration (major axis sensitivity mismatch, other axis sensitivity, offset, etc.) can be achieved, and the calibration error of the plurality of sensor units 300 can be reduced to Since it can be reduced in the previous stage instead of being processed in the signal space separation stage, the magnetic field component to be measured can be extracted with higher accuracy.

FIG. 12 shows a flow in which the magnetocardiography apparatus 10 according to this embodiment calculates the index ε and performs control based on the index ε. At step 1210, the calibration calculation section 920 calibrates the measurement data based on the above (Formula 5) to generate the magnetic field measurement data.

At step 1220, the signal space separation section 960 separates the spatial distribution of the magnetic field into signals according to the flow of FIG. Then, the signal space separation section 960 supplies the signal separation result to the index calculation section 970 . At this time, the signal space separation section 960 may supply, for example, the output vector Φ, the matrix S, and the vertical vector X to the index calculation section 970 as a result of the signal separation.

At step 1230 , the index calculator 970 calculates an index ε indicating the accuracy of calibration in the calibration calculator 920 based on the result of signal separation by the signal space separator 960 . For example, the index calculator 970 may calculate the index ε by subtracting the inner product of the matrix S and the vertical vector X from the output vector Φ, as shown in the following equation. That is, the index calculation unit 970 maps the output vector Φ of the magnetic field measured using the magnetic sensor array 210 at a certain time to the subspace spanned by the basis vector S=[Sin, Sout] using the least squares method. The error is calculated for each component of the vector, and this is used as the index ε. Then, the index calculator 970 supplies the calculated index ε to the index output unit 980 .

Next, the index output unit 980 causes the display unit to display the index ε. Then, the index output section 980 supplies the index ε to the failure determination section 990 . At this time, the index output unit 980 may further supply the index ε to another device via the network.

At step 1240, the failure determination unit 990 determines whether the index ε is within a predetermined reference range. For example, the failure determination unit 990 determines whether or not the square of the index is less than the square of the predetermined threshold E_Th, as shown in the following equation. That is, the failure determination section 990 determines whether or not the magnitude of the vector of the index ε is less than the predetermined threshold E_th.

Here, the index ε is the vector component corresponding to the sum of the number of the plurality of magnetic sensor cells 220 of the magnetic sensor array 210 multiplied by three and the number of the gradient magnetic fields calculated by the gradient magnetic field calculator 940. consists of The failure determination section 990 may, for example, calculate an index for each of a plurality of components and determine whether or not the average thereof is within a predetermined reference range. Alternatively, the fault determination unit 990 calculates the index of the component with the largest magnitude, the index of the component with the smallest magnitude, and the median value is within a predetermined reference range.

If the failure determination unit 990 determines that the index ε is within the predetermined reference range, the failure determination unit 990 determines that the calibration calculation unit 920 has calibrated with high accuracy, and terminates the process. That is, since the failure determination unit 990 has been calibrated with high accuracy by the calibration calculation unit 920, the failure determination unit 990 determines that the measurement results of the magnetocardiography apparatus 10 are highly reliable, and does not request further processing.

On the other hand, if it is determined in step 1240 that the index ε is not within the predetermined reference range, failure determination section 990 determines in step 1250 whether the number of times of calibration in calibration calculation section 920 is within the predetermined number of times. Determine whether or not.

Then, if the number of times of calibration is not within the predetermined number of times, in step 1260, the failure determining section 990 determines that the magnetocardiography apparatus 10 has failed, and terminates the process. At this time, the failure determination unit 990 may display on the display unit or notify by sound that the magnetocardiography device 10 has a failure. Further, the failure determination unit 990 may estimate the failure location of the magnetocardiography device 10 from the index for each component of the vector calculated in step 1230 and output it. At this time, the failure determination section 990 may output information specifying the magnetic sensor cell 220 or the sensor section 300 corresponding to the index determined to be out of the range of the predetermined criteria. Further, the failure determination section 990 may output an index map in which indices of respective vector components are mapped to corresponding magnetic sensor cells 220 and sensor sections 300, for example.

On the other hand, if it is determined in step 1250 that the number of times of calibration is within the predetermined number of times, failure determination section 990 instructs calibration calculation section 920 to recalibrate the measurement data. Then, in step 1270, the calibration calculation unit 920 changes the calibration parameters, returns the process to step 1210, performs recalibration using the changed calibration parameters, and continues the process. At this time, the calibration calculation unit 920 may, for example, measure the environmental magnetic field again, readjust the main axis sensitivity, the other axis sensitivity, and the offset of the sensor unit 300 to change the calibration parameters.

The flow of FIG. 12 may be performed when the subject is at the measurement position of the magnetocardiographic measuring device 10, or may be performed in advance before the subject comes to the measuring position of the magnetocardiographic measuring device 10. . In this case, the failure determination section 990 may set the threshold E_Th used for failure determination to different values depending on whether the subject is present or not.

As described above, the magnetocardiography apparatus 10 according to the present embodiment calculates the index ε indicating the accuracy of calibration in the calibration calculation unit 920, and performs control based on the index ε. Thus, according to the magnetocardiography apparatus 10 according to the present embodiment, it is possible to grasp whether or not the calibration calculation section 920 has calibrated with high accuracy. Further, according to the magnetocardiography apparatus 10 according to the present embodiment, by displaying the index ε, the reliability of the measurement result of the magnetocardiography apparatus 10 can be informed to the user. Further, according to the magnetocardiography apparatus 10 according to the present embodiment, it is possible to determine the failure of the magnetocardiography apparatus 10 based on the index ε and estimate the location of the failure. In addition, according to the magnetocardiography apparatus according to the present embodiment, the calibration calculation unit 920 recalibrates the measurement data based on the index ε calculated by the index calculation unit 970, so that the heart is accurately calibrated. It can measure magnetism.

FIG. 13 shows an example in which the magnetocardiography apparatus 10 according to the modification of the present embodiment measures magnetocardiography using a magnetic sensor array 210 configured to form an internal space. In this modified example, the magnetic sensor array 210 is configured by arranging a plurality of magnetic sensor cells 220 so as to form an internal space surrounding at least part of the chest of the subject (subject). In this figure, as an example, a plurality of magnetic sensor cells 220 are arranged on one side (X-axis direction) facing the front of the object to be measured and two sides (Z-axis direction) facing the left and right sides of the object to be measured. By placing the object to be measured in the inner space of a plurality of magnetic sensor cells 220 arranged in a U shape, at least part of the chest of the object to be measured constitutes the magnetic sensor array 210. Surrounded by a plurality of magnetic sensor cells 220 . That is, the plurality of magnetic sensor cells 220 may be arranged in a generally arcuate cross-sectional view along the chest of the object to be measured around the center of gravity of the object to be measured, as indicated by the dashed lines in this figure. As a result, the magnetic sensor array 210 can have sensor units arranged not only in one direction facing the heart, but also in multiple directions, and can sense magnetocardia in multiple directions. Also, in this case, the central angle of the arc may be greater than 180°. Thereby, the magnetic sensor array 210 can sense the heart from four directions, ie, the front, left, right, and back sides.

FIG. 14 shows an example in which the magnetocardiography apparatus 10 according to another modification of the present embodiment measures magnetocardiography using a magnetic sensor array 210 configured to form an internal space. In this figure, as an example, a plurality of magnetic sensor cells 220 are arranged on one side (X-axis direction) facing the front and back of the object to be measured and one side (Z-axis direction) facing the left side of the object to be measured. By arranging the object to be measured in the internal space of a plurality of magnetic sensor cells 220 arranged in a U shape, at least part of the chest of the object to be measured constitutes the magnetic sensor array 210. surrounded by a plurality of magnetic sensor cells 220 . As a result, the magnetic sensor array 210 can sense the heart located on the left side of the subject by arranging the plurality of magnetic sensor cells 220 near the heart.

13 and 14 show an example in which a plurality of magnetic sensor cells 220 are aligned along one side of the U shape, but the present invention is not limited to this. The plurality of magnetic sensor cells 220 may be arranged stepwise on at least one side forming the internal space. Further, in the above description, the plurality of magnetic sensor cells 220 are arranged at lattice points in the three-dimensional lattice space. Although the case where they are arranged is shown as an example, it is not limited to this. At least some adjacent cells of the plurality of magnetic sensor cells 220 may be arranged with a deviation smaller than the unit size of the cells.

When the magnetic sensor array 210 as shown in FIGS. 13 and 14 is used, the magnetocardiography apparatus 10 according to the present embodiment virtually supplements magnetic field information by signal separation of the spatial distribution of the magnetic field using the gradient magnetic field. high affinity with That is, as shown in FIGS. 13 and 14, the chest of the object to be measured is surrounded by a plurality of magnetic sensor cells 220 as long as physical restrictions allow, and the measurement is performed using a plurality of magnetic sensor cells 220 arranged in this manner. By separating the signal from the spatial distribution of the magnetic field using the gradient magnetic field and virtually supplementing the magnetic field information, the magnetocardiogram can be measured in a state closer to the ideal.

Various embodiments of the invention may be described with reference to flowchart illustrations and block diagrams, where blocks refer to (1) steps in a process in which operations are performed or (2) devices responsible for performing the operations. may represent a section of Certain steps and sections may be implemented by dedicated circuitry, programmable circuitry provided with computer readable instructions stored on a computer readable medium, and/or processor provided with computer readable instructions stored on a computer readable medium. you can Dedicated circuitry may include digital and/or analog hardware circuitry, and may include integrated circuits (ICs) and/or discrete circuitry. Programmable circuits include logic AND, logic OR, logic XOR, logic NAND, logic NOR, and other logic operations, memory elements such as flip-flops, registers, field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), etc. and the like.

Computer-readable media may include any tangible device capable of storing instructions to be executed by a suitable device, such that computer-readable media having instructions stored thereon may be designated in flowcharts or block diagrams. It will comprise an article of manufacture containing instructions that can be executed to create means for performing the operations described above. Examples of computer-readable media may include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, and the like. More specific examples of computer readable media include floppy disks, diskettes, hard disks, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM or flash memory), Electrically Erasable Programmable Read Only Memory (EEPROM), Static Random Access Memory (SRAM), Compact Disc Read Only Memory (CD-ROM), Digital Versatile Disc (DVD), Blu-ray (RTM) Disc, Memory Stick, Integration Circuit cards and the like may be included.

The computer readable instructions may be assembler instructions, Instruction Set Architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state setting data, or object oriented programming such as Smalltalk, JAVA, C++, etc. language, and any combination of one or more programming languages, including conventional procedural programming languages, such as the "C" programming language or similar programming languages. good.

Computer readable instructions may be transferred to a processor or programmable circuitry of a general purpose computer, special purpose computer, or other programmable data processing apparatus, either locally or over a wide area network (WAN), such as a local area network (LAN), the Internet, or the like. ) and may be executed to create means for performing the operations specified in the flowcharts or block diagrams. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, and the like.

FIG. 15 illustrates an example computer 2200 in which aspects of the invention may be implemented in whole or in part. Programs installed on the computer 2200 may cause the computer 2200 to function as one or more sections of an operation or apparatus associated with an apparatus according to embodiments of the invention, or may Sections may be executed and/or computer 2200 may be caused to execute processes or steps of such processes according to embodiments of the present invention. Such programs may be executed by CPU 2212 to cause computer 2200 to perform certain operations associated with some or all of the blocks in the flowcharts and block diagrams described herein.

Computer 2200 according to this embodiment includes CPU 2212 , RAM 2214 , graphics controller 2216 , and display device 2218 , which are interconnected by host controller 2210 . Computer 2200 also includes input/output units such as communication interface 2222, hard disk drive 2224, DVD-ROM drive 2226, and IC card drive, which are connected to host controller 2210 via input/output controller 2220. there is The computer also includes legacy input/output units such as ROM 2230 and keyboard 2242 , which are connected to input/output controller 2220 through input/output chip 2240 .

CPU 2212 operates according to programs stored in ROM 2230 and RAM 2214, thereby controlling each unit. Graphics controller 2216 retrieves image data generated by CPU 2212 into itself, such as a frame buffer provided in RAM 2214 , and causes the image data to be displayed on display device 2218 .

Communication interface 2222 communicates with other electronic devices over a network. Hard disk drive 2224 stores programs and data used by CPU 2212 within computer 2200 . DVD-ROM drive 2226 reads programs or data from DVD-ROM 2201 and provides programs or data to hard disk drive 2224 via RAM 2214 . The IC card drive reads programs and data from IC cards and/or writes programs and data to IC cards.

ROM 2230 stores therein programs that are dependent on the hardware of computer 2200, such as a boot program that is executed by computer 2200 upon activation. Input/output chip 2240 may also connect various input/output units to input/output controller 2220 via parallel ports, serial ports, keyboard ports, mouse ports, and the like.

A program is provided by a computer-readable medium such as a DVD-ROM 2201 or an IC card. The program is read from a computer-readable medium, installed in hard disk drive 2224 , RAM 2214 , or ROM 2230 , which are also examples of computer-readable medium, and executed by CPU 2212 . The information processing described within these programs is read by computer 2200 to provide coordination between the programs and the various types of hardware resources described above. An apparatus or method may be configured by implementing the manipulation or processing of information in accordance with the use of computer 2200 .

For example, when communication is performed between the computer 2200 and an external device, the CPU 2212 executes a communication program loaded into the RAM 2214 and sends communication processing to the communication interface 2222 based on the processing described in the communication program. you can command. The communication interface 2222 reads transmission data stored in a transmission buffer processing area provided in a recording medium such as the RAM 2214, the hard disk drive 2224, the DVD-ROM 2201, or an IC card under the control of the CPU 2212, and transmits the read transmission data. Data is transmitted to the network, or received data received from the network is written to a receive buffer processing area or the like provided on the recording medium.

In addition, the CPU 2212 causes the RAM 2214 to read all or necessary portions of files or databases stored in external recording media such as a hard disk drive 2224, a DVD-ROM drive 2226 (DVD-ROM 2201), an IC card, etc. Various types of processing may be performed on the data in RAM 2214 . CPU 2212 then writes back the processed data to the external recording medium.

Various types of information, such as various types of programs, data, tables, and databases, may be stored on recording media and subjected to information processing. CPU 2212 performs various types of operations on data read from RAM 2214, information processing, conditional decision making, conditional branching, unconditional branching, and information retrieval, as specified throughout this disclosure and by instruction sequences of programs. Various types of processing may be performed, including /replace, etc., and the results written back to RAM 2214 . In addition, the CPU 2212 may search for information in a file in a recording medium, a database, or the like. For example, if a plurality of entries each having an attribute value of a first attribute associated with an attribute value of a second attribute are stored in the recording medium, the CPU 2212 determines that the attribute value of the first attribute is specified. search the plurality of entries for an entry that matches the condition, read the attribute value of the second attribute stored in the entry, and thereby associate it with the first attribute that satisfies the predetermined condition. an attribute value of the second attribute obtained.

The programs or software modules described above may be stored in a computer readable medium on or near computer 2200 . Also, a recording medium such as a hard disk or RAM provided in a server system connected to a dedicated communication network or the Internet can be used as a computer-readable medium, thereby providing the program to the computer 2200 via the network. do.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the scope of claims that forms with such modifications or improvements can also be included in the technical scope of the present invention.

The execution order of each process such as actions, procedures, steps, and stages in the devices, systems, programs, and methods shown in the claims, the specification, and the drawings is particularly "before", "before etc., and it should be noted that they can be implemented in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the specification, and the drawings, even if the description is made using "first," "next," etc. for the sake of convenience, it means that it is essential to carry out in this order. not a thing

10 magnetocardiographic measuring device 100 main unit 110 magnetic sensor unit 120 head 130 base unit 140 pole unit 150 information processing unit 210 magnetic sensor array 220 magnetic sensor cell 230 sensor data collecting unit 232 AD converter 234 clock generator 300 sensor unit 520 magnetic sensor 530 magnetic field generating unit 532 amplifier circuit 534 coil 540 output unit 710 magnetoresistive effect elements 720, 730 magnetic flux converging plate 900 sensor data processing unit 910 measurement data acquisition unit 920 calibration calculation unit 930 data output unit 940 gradient magnetic field calculation unit 950 basis vector storage Unit 960 Signal space separation unit 970 Index calculation unit 980 Index output unit 990 Failure determination unit 2200 Computer 2201 DVD-ROM
2210 host controller 2212 CPU
2214 RAM
2216 graphics controller 2218 display device 2220 input/output controller 2222 communication interface 2224 hard disk drive 2226 DVD-ROM drive 2230 ROM
2240 input/output chip 2242 keyboard

Claims (11)

a magnetic sensor array configured by three-dimensionally arranging a plurality of magnetic sensor cells each capable of detecting an input magnetic field in three axial directions;
a measurement data acquisition unit that acquires measurement values based on the input magnetic field including magnetocardiography generated by electrical activity of the heart;
a gradient magnetic field calculator that calculates a gradient magnetic field using a plurality of measured values measured between the plurality of magnetic sensor cells;
a signal space separation unit that separates the spatial distribution of the input magnetic field into the magnetic field of the heart and the environmental magnetic field using the gradient magnetic field;
A magnetocardiography device. The signal space separating unit divides the plurality of 2. The magnetocardiographic measurement device according to claim 1, wherein the spatial distribution of the input magnetic field is separated into signals using at least a magnetic field gradient vector calculated using a plurality of magnetic field signal vectors output between the magnetic sensor cells of the . 3. The magnetocardiographic measurement apparatus according to claim 2, wherein said signal space separation unit separates signals from the spatial distribution of said input magnetic field using said magnetic field gradient vector and said magnetic field signal vector as basis vectors. each of the plurality of magnetic sensor cells,
a magnetic sensor;
a magnetic field generator that provides the magnetic sensor with a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor;
an output unit for outputting an output signal according to the current that the magnetic field generation unit flows to generate the feedback magnetic field;
The magnetocardiography apparatus according to any one of claims 1 to 3, comprising: 5. The magnetocardiography apparatus according to claim 4, wherein said magnetic sensor has a magnetoresistive element. Each of the plurality of magnetic sensor cells further has two magnetic flux concentrators arranged at both ends of the magnetoresistive effect element, and the magnetoresistive effect element is arranged at a position sandwiched between the two magnetic flux concentrators. The magnetocardiography device according to claim 5, wherein 7. The magnetocardiographic measuring apparatus according to claim 6, wherein a coil for generating said feedback magnetic field is wound so as to surround said magnetoresistive effect element and said two magnetic flux concentrators. further comprising a plurality of AD converters that convert the outputs of the plurality of magnetic sensor cells from analog to digital and output the measured values;
8. The magnetocardiographic measurement apparatus according to claim 1, wherein said plurality of AD converters perform AD conversion according to a common sampling clock. 9. The magnetic sensor array according to any one of claims 1 to 8, wherein the plurality of magnetic sensor cells are arranged so as to form an internal space surrounding at least a portion of the chest of the subject. The magnetocardiography device according to . 10. The magnetocardiographic measurement apparatus according to claim 9, wherein said plurality of magnetic sensor cells are arranged in a generally arcuate cross-sectional view around the center of gravity of said object to be measured along the chest of said object to be measured. 11. The magnetocardiography apparatus according to claim 10, wherein the central angle of the arc is greater than 180[deg.].

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